1. Field of the Invention
The present invention relates to integrated read/write perpendicular recording heads. More specifically, the invention relates to locating a read element between the main pole and the flux return pole portions of the writer.
2. Description of the Related Art
Recording heads for use with magnetic storage media have typically been of the longitudinal type, utilizing a pair of opposing write poles with their tips in close proximity to each other at the bottom surface of the recording head. The two poles are connected typically at the top by a yoke, typically made of the same ferromagnetic material as the poles. A coil is located in close proximity to one of the two opposing poles. When current passes through the coil, magnetic flux is induced in the yoke which produces a magnetic field with a bubble-like contour, across a gap separating the two poles. A portion of the magnetic flux across the write gap will pass through the magnetic storage medium, thereby causing a change in the magnetic state within the magnetic storage medium where the head field is higher than the media coercive force. The media coercive force is chosen high enough so that only the head fields across a narrow gap of a thin film inductive head, flowing with a slider on a air bearing between the surfaces of the disk and the slider, modify the bits of information on the storage media.
The bits of information are recorded on the disk along concentric tracks that are separated by guard bands. The width of the track plus that of the guard-band in which no information is stored defines the track density. The length of the bit along the track defines the linear density. The total storage capacity is directly proportional to the product of track density and linear density. The increase in linear density also enhances the data transfer rate. The demand for higher storage capacity and higher data rates led to the redesign of various components of disk drives.
The recording densities possible with longitudinal recording are limited to approximately 50 to 100 G bit/inch2, because at higher recording densities, superparamagnetic effects result in magnetic instabilities within the magnetic storage medium.
Perpendicular recording has been proposed to overcome the recording density limitations of longitudinal recording. Perpendicular recording heads for use with magnetic storage media typically include a pair of magnetically coupled poles, consisting of a main write pole having a small bottom surface area, and a flux return pole having a large bottom surface area. A coil is located adjacent to the main write pole, for inducing a magnetic field between that pole and a soft underlayer. The soft underlayer is located below the recording layer of the magnetic storage medium and enhances the amplitude of the field produced by the main pole. This in turn allows the use of media with higher coercive force, consequently, more stable bits can be stored in the media. In the recording process, an electrical current in the coil energizes the main pole, which produces a magnetic flux density field. The image of this field is produced in the soft underlayer, such that about double the field strength is produced in the magnetic media. The flux density that diverges from the tip into the soft underlayer returns to the main pole through the return flux pole. The return pole is located sufficiently far apart from the main pole, such that the soft material of the return pole does not affect the magnetic flux of the main pole, which is directed vertically into the hard layer and soft underlayer. Significantly higher recording densities may therefore be used before magnetic instabilities become an issue.
Originally, retrieval of the information stored in magnetic disks was accomplished with an inductive head. The rate of change of magnetic field passing through the gap between the poles of the recording head would induce a voltage across the coils. The voltage signal was directly proportional to the rate of change of the field across the gap. Since the 80""s, magnetoresistive heads replaced thin film inductive heads for the reading process because they produce considerably higher change of voltage while sensing magnetic flux incoming from magnetic patterns of the media.
To overcome the limitations of inductive reading, various magnetoresistive (MR) read elements have been proposed. Such read elements are typically located between a pair of shields made from soft magnetic material similar to that used in the inductive heads. The shields define the linear resolution of the read head, as they prevent that the sensor from being affected by magnetic fields other than that from the bit being read.
For a decade, the magnetoresistive elements consisted of Permalloy thin films and exhibited an anisotropic magnetoresistive (AMR) effect. As the areal density requirement in disk drives approached 10 Gbit/in2, the AMR heads could not provide enough sensitivity for adequate signal to noise ratio even if they used extremely high electrical current. A new magnetoresistive effect, discovered in the early 80""s needed to be applied. The magnetoresistive (MR) read element that has been adopted by most of the industry for magnetic disk drives is the spin valve sensor. The spin valve provides a spin dependent giant magnetoresistance effect with a very thin sensor layer. Hence, it exhibits enough sensitivity for current disk drives. The spin valve is generally composed of a pair of ferromagnetic layers having a nonmagnetic layer therebetween. One of the ferromagnetic layers is adjacent and in direct contact with an antiferromagnetic layer. The antiferromagnetic layer produces a unidirectional anisotropic field in the ferromagnetic layer. The unidirectional field is strong enough to remain constant during the head operation. The combination of the ferromagnetic layer and adjacent antiferromagnetic layer is commonly known as the pinned layer, with the opposite ferromagnetic layer known as the free layer. When the spin valve is exposed to a magnetic field, the orientation of the magnetization of the free layer will change accordingly. The change in the orientation of the magnetization of the free layer relative to the pinned layer will alter the spin dependent scattering of conduction electrons, thereby increasing or decreasing the resistance of the spin valve element. The change in resistance produces a corresponding change in the voltage signal for an applied electrical current. A constant voltage level indicates a binary xe2x80x9c0xe2x80x9d and a changing voltage level indicates a binary xe2x80x9c1.xe2x80x9d
Despite the fact that the spin valve provided enough sensitivity for 10 Gbit/in2 areal density, the rapid pace of storage capacity increase required for current applications could not be overlooked. A dual spin valve was then proposed, wherein a second pinned layer and electroconductive layer are placed on the opposite side of the free layer. The dual spin valve (DSV) could provide higher signal output than the spin valve. The drawback of the DSV consisted in the need for a synthetic antiferromagnet (SAF) to overcome the fields of the two reference layers. This requirement resulted in a structure considerably thicker than the spin valve itself, which led to a large increase in minimum shield-to-shield spacing. The shield-to-shield spacing of the SV or the DSV, corresponding approximately to twice the read-back gap length, ultimately defines the read head linear resolution. Hence, the DSV was not pursued, because it exhibited lower signal output at higher linear densities.
The need for increasing the speed of the read and write operations, combined with the increasing storage density within the magnetic storage media, make it desirable to integrate a read head with very high linear resolution and sensitivity in very close proximity to the write head. The spatial distance between the write and read head require complex arm operations to correct it and increase seek time. For these reasons, some recording heads use a shared pole integrated scheme, in which the flux return pole of the writer functions as one of two opposing shields of the reader.
There are several important considerations for integrating the read and write portions of a recording head. The read element must not be placed in a location where it will be exposed to the strong magnetic fields generated by the opposing write poles. Exposing the read element to such strong magnetic fields creates a risk of electrostatic damage to the read elements, and could possibly change the default magnetizations of the ferromagnetic layers within the read elements. Furthermore, steps must be taken to ensure that magnetic fields adjacent to the magnetic field of the domain currently being read do not affect the read element. Therefore, either shields must be provided for the read elements, or a read element that is not sensitive to magnetic fields adjacent to the fields being read are required.
Accordingly, there is a need for a recording head having integrated read/write portions. Additionally, there is a need to protect the read element within such a recording head from the magnetic fields generated from the write portion of the recording head. Furthermore, there is a need to protect the read element within such a recording head from being influenced by magnetic fields adjacent to the magnetic fields currently being read. Finally, the shields of the read head, if in close proximity of the recording main pole, should not affect the side writing and the field amplitude and contour in the storage layer.
The present invention is a perpendicular recording head integrating an unshielded magnetoresistive read head provided with high sensitivity and high linear resolution for very high performance hard disk drives.
A perpendicular recording head includes a main pole, a flux return pole magnetically coupled to the main pole, and an electrically conductive coil adjacent to the main pole. The bottom of the flux return pole has a surface area greatly exceeding the surface area of the main pole""s tip. The recording head includes a read element, a differential dual spin valve, located between the main and opposing poles. Electrical conductor leads are located at each end of the differential dual spin valve.
The structure and function of a differential dual spin valve is best understood through an explanation of a single spin valve and a dual spin valve. The spin valve is generally composed of a pair of ferromagnetic layers having a nonmagnetic layer therebetween. One of the ferromagnetic layers is adjacent and in direct contact with an antiferromagnetic layer. The antiferromagnetic layer produces a unidirectional anisotropy field in the ferromagnetic layer, which is strong enough to remain constant during the head operation. The combination of the ferromagnetic layer and adjacent antiferromagnetic layer is commonly known as the pinned layer, with the opposite ferromagnetic layer known as the free layer. When the spin valve is exposed to a magnetic field, the orientation of the magnetization of the free layer will change accordingly. The change in the orientation of the magnetization of the free layer relative to the pinned layer will alter the spin dependent scattering of conduction electrons, thereby increasing or decreasing the resistance of the spin valve element. The change in resistance produces a change in a voltage signal for an applied electrical current. A constant voltage level indicates a binary xe2x80x9c0xe2x80x9d and a changing voltage level indicates a binary xe2x80x9c1.xe2x80x9d
A dual spin valve consists of one free layer and two pinned layers. The free layer is located in the center of two opposing pinned layers, each separated from the free layer by a Cu spacer. The pinned layers incorporate a synthetic antiferromagnetic layer as an antiferromagnetic layer. The synthetic antiferromagnet comprises two ferromagnetic layers that are indirectly antiferromagnetically coupled through a metallic interlayer, for example, Ru.
The spin valve head and the dual spin valve head incorporate a pair of shields located at both ends of the MR element. Electrical leads and associated insulators are located between the read element and each shield, being dimensioned and configured to apply a sense current across the read element. The sensor must be electrically insulated from the shields. The thickness of the electrical insulator plus half of the read element thickness define the reproduce gap of the head. Good electrical insulation between the read element and the shields must be provided because the electrical current carried by the leads flows parallel to the layers of the sensor, in the so-called current in the plane (CIP) geometry. In this geometry, electrical contact between the shields and the read-element would produce shunting of current and signal amplitude loss.
A differential dual spin valve includes a pair of spin valves positioned end to end, so that the pinned layers are on the outside of the complete structure, and the free layers are towards the center. The two free layers are separated by an electrically conductive gap film that physically defines the reproduce gap. That is to say that the head does not require shields for linear resolution. Like in the spin valve head, the default magnetization of each free layer will align along the track width of the sensor, which is aligned parallel to the recording track of the media. The magnetizations of the pinned layers are aligned orthogonal to the track-width and antiparallel to each other. Hence, when the free layers rotate together toward the same orientation in response to a uniform field, in one spin valve the free layer will be rotating from orthogonal to parallel to the reference layer and in the other spin valve, the free layer will be rotating from orthogonal to antiparallel to the pinned layer. In the current perpendicular to the plane (CPP) geometry, the electrical current flows perpendicular to the plane of the layers. The net voltage across the two spin valves, electrically connected in series through the metallic gap spacer, is given by the sum of the variation of resistance in each spin valve multiplied by the applied current. Consequently, the sum of the responses of two spin valves electrically connected in series, having antiparallel pinned layers, yield zero variation of voltage when their free layer magnetizations are rotated by the same angle amount together toward the same direction. On the other hand, when the gap of the differential dual spin valve is placed above a change in the orientation of the magnetization within the magnetic storage medium, the spin valves will sense opposite oriented magnetic fields, producing rotations of magnetizations toward opposite orientations. Hence, one free layer will rotate to parallel to the pinned layer while the other free layer will rotate parallel to its reference layer. The total change of resistance will correspond to the sum of that of each spin valve.
When reading from a magnetic storage medium having a constant magnetization, the magnetization in each free layer will be oriented to conform to the magnetization of that portion of the magnetic storage medium directly below each individual free layer. Therefore, pinned and free layers within one portion of the differential dual spin valve will have parallel orientations, and the magnetizations within the pinned and free layers of the other portion of the differential dual spin valve will have antiparallel magnetizations. One portion of the differential dual spin valve will therefore have minimum resistance, and the other portion will have maximum resistance. The result is that the overall differential dual spin valve structure will have a medium level of resistance. When the magnetization within the storage medium changes from upward to downward, or from downward to upward, the spin valves will briefly be located over domains of the magnetic storage medium having opposing magnetizations. The magnetizations within the free layers will therefore rotate to correspond to the magnetizations within the magnetic storage medium domains over which the spin valves are located. Resistance within both differential dual spin valve portions will therefore either be minimized or maximized, depending upon whether the magnetizations of the free layer and corresponding pinned layer are parallel or antiparallel. It follows that minimized resistance in both portions of the differential dual spin valve results in minimized resistance for the entire differential dual spin valve structure, and maximized resistance in both portions of the differential dual spin valve results in maximized resistance for the entire spin valve structure. This resistance will be tested by a sensed current passed through the differential dual spin valve. The electrical contacts may be located in contact with the pinned layers on each end of the differential dual spin valve, resulting in the sense current being applied perpendicular to the plane of the layers of the differential dual spin valve (CPP).
The combination of a perpendicular recording head with a differential dual spin valve resolves many of the difficulties that would otherwise be associated with such an integrated read/write head. Whereas a longitudinal write head directs magnetic flux across the gap between the opposing write poles (and therefore across any read elements located between the poles), a perpendicular recording head directs magnetic flux downward through an upper recording layer of a magnetic storage medium, across through a soft underlayer of the storage medium, and then back to the flux return pole to form a complete loop. The return pole must be located sufficiently far apart from the main pole to not disturb the magnetic flux path from the main pole into the storage media. Likewise, shields near the main pole needed to be placed far apart from the main pole for the exact same reason. On the other hand, an unshielded read element like the differential dual spin valve above described could be incorporated between the main and opposing poles of a perpendicular recording head. In this integration scheme the read element is located between the write head poles but apart from each pole by a factor of three to four times the distance between the poles and the soft underlayer. With this structure, the strong magnetic fields generated during a write operation will not cause deterioration in the read head. Therefore, a differential dual spin valve may be utilized in a location where the write poles provide only limited magnetic shielding, and wherein an additional ferromagnetic shielding structure could distort the write field contour.
It is therefore an aspect of the present invention to provide a perpendicular recording head having integrated read and write portions.
It is another aspect of the present invention to provide a perpendicular recording head having a read element disposed between the main write pole and the flux return pole.
It is a further aspect of the present invention to provide an integrated read/write recording head wherein magnetic fields generated by the write poles will not adversely affect the read element.
It is another aspect of the present invention to provide an integrated read/write perpendicular recording head having a read element capable of functioning with only minimal magnetic shielding.
It is a further aspect of the present invention to provide an integrated read/write perpendicular recording head wherein the main write pole and read element are separated by a small distance for high data rate applications.
It is a further aspect of the present invention to provide an integrated read/write perpendicular recording head for very high areal density and very high data transfer rate applications wherein the main write pole produces strong magnetic fields, capable of switching the magnetization of a storage layer provided with very high coercive force, and the read head provides a sensitivity comparable to or higher than that of a dual spin valve but with a considerably higher linear resolution.